1. Field of the Invention
The present invention relates generally to spacecraft operations for purpose of generating on-board power, and more particularly, to a system and method for deploying and using a satellite solar array.
2. Description of the Related Art
Solar arrays are used to collect solar energy for use in operational satellites. There are two general approaches to arranging the solar arrays on an operational earth-observing satellite. The first approach (otherwise known as the articulated array technique) is to locate the solar array with its principal axis orthogonal to the principal axis of the observing instrument package (typically at or near the Earth's nadir) and use sun tracking mechanisms to track the Sun and active control systems to orient the solar array to present a surface that is normal to the vector between the Sun and the satellite. The second approach uses fixed solar arrays that are orthogonal to the observing axis. However, in the second approach, the satellite's attitude is controlled so as to present their surface normal to the Sun vector. This is known as the fixed array technique.
When using the articulated array method, the solar array may cause objectionable disturbances to be coupled into the earth sensing instruments thereby detracting from the quality of information obtained from the system. These disturbances arise from two factors inherent is the design of the solar array system, a) the mechanisms (motors, etc.) used to drive the arrays during sun tracking cause mechanical noise or vibration of the solar array; b) attitude changes of the space vehicle required to position the satellite for viewing a desired area of the earth excite vibration modes of the solar arrays. Both of these disturbance sources unavoidably couple into the instrument assembly thereby reducing the quality of information provided by the sensing system.
In the fixed array technique, the structural dynamics problems are avoided by building a rigid fixed array coupled by a bracing structure anchoring the far end of each array to the structure of the satellite. By strengthening and bracing these arrays the disturbances can be eliminated to the degree required; the downside of this approach is that the satellite must be rotated away from the viewing attitude in order that the arrays face the sun during the energy collection period. Thus this method results in a low utility factor of the solar arrays and limits the observing duty factor (since observations are typically not possible when the satellite is oriented to collect solar energy). In practice, arrangements of this design result in a very low duty factor depending on specifics of the orbit, the array size and various load factors.
What is needed is an solar array arrangement that provides adequate power without objectionable disturbances, whether from solar array articulations or from satellite body motion, and a method for deploying such a solar array. The present invention satisfies these needs.